The devices and methods herein relate to the design of via chains and serpentine/comb testable structures, and more specifically, to structures and methods that provide lower resistance and more accurate circuit integrity determination when testing via structures.
An integrated circuit (IC) is a semiconductor device containing many small, interconnected components such as diodes, transistors, resistors, and capacitors. These components function together to enable the IC to perform a task, such as control an electronic device, or perform logic operations. ICs are found in computers, calculators, cellular telephones, and many other electronic devices.
ICs and other semiconductor devices are fabricated on small rectangles, known as “dies,” which are filled with multiple layers of the components, such as transistors, resistors, and capacitors, during the fabrication process. The connections between the layers are known as vias. In integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different layers. Multiple vias may be coupled together in what may be referred to as a “via chain” connecting one conductive region in an IC to another conductive region in the same or an adjacent IC.
A manufacturing error in one of the components may render an IC or semiconductor device incapable of functioning properly. For example, consider a memory device containing several ICs. If a transistor within one of the ICs fails to function properly, the memory device may produce memory errors. Vias are also subject to manufacturing errors. When a manufacturing error occurs in a via, the via may not conduct properly and thus may prohibit an IC from functioning correctly. For instance, an open via or a partially open via is a break in the circuit, which may prohibit a device from functioning as designed. An open via may have a high or infinite resistance, and a partially open via may have a higher than average resistance. On the other hand, the via could be shorted to a neighbor interconnect line or via, which may also prohibit a device from functioning as designed. Therefore, testing via structures is a fundamental aspect of IC production and reliability.